1. Field of the Invention
This invention relates to a method for producing a blue phosphor. More particularly, the invention relates to a blue phosphor which has high color purity, high luminance, high chemical stability, and a low crystallization temperature, and which is suitable for use in displays such as FED (field emission displays), PDP (plasma displays), and EL (electroluminescence) displays, or for use in the excitation of near-ultraviolet LED (light emitting diodes).
2. Description of the Related Art
As blue phosphors for inorganic EL displays, (1) SrS:Ce, (2) MGa2S4:Ce (M=Sr, Ca), (3) BaAl2S4:Eu, (4) Ba2SiS4:Ce and the like have been known so far. As blue phosphors for LED lamps, (5) (Ba,Mg)Al10O17:Eu, (6) Sr5(PO4)3Cl:Eu and the like are known.
The above (1) SrS:Ce gives a relatively high luminance, but is bluish green in tone, and has poor color purity. Moreover, lattice defects are apt to form in the material, and the tone of this material varies widely. With the (2) MGa2S4:Ce (M=Sr, Ca), color purity is satisfactory, but luminance is low. Furthermore, this material has a multi-component composition, involving troublesome control over its composition. In the case of the (3) BaAl2S4:Eu, color purity is satisfactory, and luminance is high, but its multi-component composition requires complicated control. Besides, this material is easily degradable in the atmosphere, and thus its chemical stability is very low. Moreover, its crystallization temperature is so high (750° C. or higher) that its use in inexpensive glass substrates is difficult. The (4) Ba2SiS4:Ce is satisfactory in color purity, high in chemical stability, and low in crystallization temperature, but is low in luminance. The (5) (Ba,Mg)Al10O17:Eu and (6) Sr5(PO4)3Cl:Eu have excitation bands in the near-ultraviolet wavelength region, and they are expected to be applicable to lamps in combination with near-ultraviolet LED. However, their conversion efficiency for light is insufficient.
It is an object of the present invention to provide a method for producing a blue phosphor which has high color purity, high luminance, high chemical stability, and a low crystallization temperature, and which is suitable for use in displays such as FED (field emission displays), PDP (plasma displays), and EL (electroluminescence) displays, or for use in the excitation of near-ultraviolet LED (light emitting diodes).